An active drive twisted nematic type liquid crystal display device (hereinafter referred to simply as "TN-LCD") using TFT element or MIM element affords an image quality comparable to a CRT as seen from the front side, in addition to the characteristics inherent in LCD such as small thickness, light weight and low power consumption. For this reason, the TN-LCD is spread widely as a display for notebook type personal computers, portable telephone and portable information terminals. However, the conventional TN-LCD inevitably involves a problem associated with a viewing angle such that there occurs change in display color or a lowering of display contrast when seen obliquely, due to refractive index anisotropy. It has keenly been desired to solve this problem, and various attempts have been made for improvement. For example, there have been proposed a method (halftone gray scale method) wherein one pixel is divided and the voltage applied to each divided pixel is changed at a certain ratio, a method (domain dividing method) wherein one pixel is divided and a rising direction of liquid crystal molecules in each divided pixel is changed, a method (IPS method) wherein a lateral electric field is applied to liquid crystal, a method (VA liquid crystal method) wherein a vertically oriented liquid crystal is driven, and a method (OCB method) wherein a bend orientation cell and an optical compensator are combined together. Developments and trial manufacture have been made in connection with these proposed methods.
Although these methods afford certain effects, it is necessary that alignment layer, electrodes and liquid crystal orientation be changed from those so far adopted.
For this change it is required to establish appropriate manufacturing techniques and new manufacturing equipment, with consequent difficulty of manufacture and increase of cost.
On the other hand, a method has been proposed wherein the viewing angle is enlarged by incorporating an optical compensating film in the conventional TN-LCD without changing at all the structure of TN-LCD itself. This method is simple and very economical because it is not necessary to make reform or increase of the TN-LCD manufacturing equipment. For this reason, this method is now attracting attention of many concerns.
In manufacturing the said film, the following are mentioned as examples of conditions required of the film material:
1) Should a high reliability worthy of commercialization in point of resistance to heat, moisture and light. PA0 2) Should be capable of being oriented under wide conditions and should afford products having little irregularity and few orientation defects. PA0 3) Should have a high film strength and a sufficient impact resistance and be superior in handleability.
However, in the case of forming a film with use of a known film material, it has been difficult for the film to fully satisfy all of the above conditions. Under the circumstances, it has been considered necessary to develop a material which satisfies the above conditions without deteriorating the optical performance of the film.